Republican White House hopeful Mitt Romney sought to create doubts about rival Newt Gingrich among South Carolina conservatives on Saturday by criticizing his highly paid work for mortgage giant Freddie Mac.

On a two-day tour of South Carolina in an attempt to dent Gingrich's big lead in the polls there, Romney all but accused Gingrich of lobbying for Freddie Mac by accepting $1.6 million in consultants' fees from an enterprise at the heart of America's housing crisis.

Gingrich has nurtured South Carolina's Tea Party conservatives to try to secure the state that holds the first primary in the South on Jan. 21 and the third overall contest in the race to determine a candidate to face Democratic President Barack Obama next November.

Romney pointed out to reporters that Gingrich had at first said he made $300,000 from Freddie Mac over an extended period and that only later was it revealed that he had earned $1.6 million from the government-sponsored enterprise.

I think as Tea Partiers concentrate on that for instance they'll say, 'Wow, this really isn't the guy that represents our views, Romney said. I think the Tea Party is anxious to have people who are outside Washington come in and change Washington, as opposed to people who have stayed in Washington for 30 or 40 years.

Gingrich's rivals are attempting to use Gingrich's work for Freddie Mac as an indictment of the former speaker of the House of Representatives, saying he reflects a Washington insider culture that needs to be changed.

Asked if he thought Gingrich's work for Freddie Mac amounted to lobbying, Romney replied: I'm going to let the lawyers decide what is and what isn't lobbying, but if it walks like a duck and it quacks like a duck, typically it's a duck.

Gingrich has denied acting as a lobbyist for Freddie Mac.

In a conference call with reporters, Gingrich pushed back against an editorial in The Wall Street Journal that focused on his Freddie Mac ties and said he did not in any way work in influence, per se.

That's an area where people have said things that are wildly inaccurate, Gingrich said.

Romney is touring South Carolina with the state's Republican governor, Nikki Haley, hoping her endorsement this week will help him curry favor with Tea Party conservatives who have long held doubts about whether Romney is true to their principles.

He said he believes he is the ideal candidate for the Tea Party movement.

I recognize that the speaker has a big lead here, Romney said of Gingrich. But I think as people take a closer and closer look, they'll recognize that I reflect more effectively the positions which they hold on key issues.

Later, at a town hall meeting in Myrtle Beach, Romney managed to get a jab in at Gingrich in answer to a question about global warming, which some conservatives do not believe is real.

I'm not planning on cutting an ad with Nancy Pelosi, he said, referring to an ad Gingrich taped in 2008 with liberal U.S. Rep. Nancy Pelosi, D-Calif., to say climate change needed to be addressed.

Romney said he believed humans contribute to global warming, but did not know how much. He acknowledged Gingrich has said the ad was a mistake.

Romney attempted to convince South Carolina's military community to side with him, a strategy that U.S. Sen. John McCain, R-Ariz., used to great effect in 2008 in winning the state's primary and going on to win the Republican presidential nomination.

South Carolina is home to eight military bases that provide jobs for thousands of military and civilian personnel. Thousands of retired military veterans are in the state, as well.

Romney vowed to build up the U.S. military if elected in place of Obama.

I want to have a military so strong that no one would ever think of testing it, he said to loud applause at a town hall event hosted by U.S. Rep. Tim Scott, R-S.C.

(Reporting By Steve Holland; Editing by Philip Barbara)